Method and relay node for mobile relay enablement

ABSTRACT

A method and relay node for managing a relay node that is moving relative to a source network node, the method receiving parameters of a target network node from a source network node at the relay node; initiating a direct attachment of the relay node to the target network node; and detaching the relay node from the source network node. Also, a method and network node for managing a relay node that is moving relative to a source network node, the method sending a handover request of a relay node from the source network node to a target network node; performing handover of a plurality of user equipments (UEs) from the source network node to the target network node, wherein the plurality of UEs are attached to the relay node, and establishing an interface between the relay node and the target network node.

FIELD OF THE DISCLOSURE

The present disclosure relates to relays and in particular relates tomobile relays.

BACKGROUND

Relay technology has been adopted in various mobile networks in aneffort to extend cell coverage and enhance system capacity. For example,such relay technology has been adopted in Third Generation PartnershipProject (3GPP) Long Term Evolution-Advanced (LTE-A) Release 10 systems.

In one embodiment, the relay node (RN) has its own cell identifier (ID)and is wirelessly connected to a serving evolved node B (eNB), referredto herein as the Donor eNB (DeNB), via the Un interface. In order tosupport RNs in a network, various network architectures may allow an S1,X2 and Un interface to be terminated at the RN.

Such architectures generally presuppose a stationary RN wirelesslyconnected with the DeNB. However, in certain cases the RN may be mobile.For example, on a train, one or more RNs may be deployed to allow mobiledevices to connect to the RN. However, the RN is itself is moving withreference to the DeNB(s).

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood with reference to thedrawings, in which:

FIG. 1 is a block diagram showing various architectures for mobilerelays;

FIG. 2 is a control plane protocol stack for the alternative 1architecture;

FIG. 3 is the user plane protocol stack for the alternative 1architecture;

FIG. 4 is a control plane protocol stack for the second alternativearchitecture;

FIG. 5 is the user plane protocol stack for the second alternativearchitecture;

FIG. 6 is a control plane protocol stack for the third alternativearchitecture;

FIG. 7 is the user plane protocol stack for the third alternativearchitecture;

FIG. 8 is a control plane protocol stack for the fourth alternativearchitecture;

FIG. 9 is the user plane protocol stack for the fourth alternativearchitecture;

FIG. 10 is a flow diagram showing X2 message exchange for mobile RNhandover in the second alternative architecture;

FIG. 11 is a flow diagram showing S1 message exchange for mobile RNhandover in the second alternative architecture;

FIG. 12 is a flow diagram showing RN start up procedures in case ofhandover failure;

FIG. 13 is a flow diagram showing X2 message exchange for mobile RNhandover in the alternative 1 architecture;

FIG. 14 is a flow diagram showing X2 message exchange for mobile RNhandover in the third alternative architecture;

FIG. 15 is a flow diagram showing a fast handover optimizationembodiment;

FIG. 16 is a flow diagram showing an RN initiated handover alternativeembodiment;

FIG. 17 is a flow diagram showing UE group mobility for RN handover;

FIG. 18 is a simplified block diagram of an example network element; and

FIG. 19 is a block diagram of an example user equipment.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure provides a method for managing a relay node thatis moving relative to a source network node, the method comprising:ensuring a target network node is capable of supporting the relay node;sending a handover request of a relay node from the source network nodeto the target network node; and establishing an interface between therelay node and the target network node.

The present disclosure further provides a source network node configuredfor managing a relay node that is moving relative to the source networknode, the source network node comprising: a processor; and acommunications subsystem, wherein the processor and communicationssubsystem cooperate to: ensure a target network node is capable ofsupporting the relay node; send a handover request of a relay node fromthe source network node to the target network node; and establish aninterface between the relay node and the target network node.

The present disclosure further provides a method for managing a relaynode that is moving relative to a source network node, the methodcomprising: sending a handover request from the source network node to atarget network node to prepare the handover at the target network node;sending a handover command from the source network node to the relaynode without waiting for an acknowledgement of the handover request fromthe target network node; and detaching the relay node from the sourcenetwork node.

The present disclosure further provides a source network node configuredfor managing a relay node that is moving relative to the source networknode, the source network node comprising: a processor; and acommunications subsystem, wherein the processor and communicationssubsystem cooperate to: send a handover request from the source networknode to a target network node to prepare the handover at the targetnetwork node; send a handover command from the source network node tothe relay node without waiting for an acknowledgement of the handoverrequest from the target network node; detach the relay node from thesource network node.

The present disclosure further provides a method for managing a relaynode that is moving relative to a source network node, the methodcomprising: receiving parameters of a target network node from thesource network node at the relay node; initiating a direct attachment ofthe relay node to the target network node; and detaching the relay nodefrom the source network node.

The present disclosure further provides a relay node configured to moverelative to a source network node, the relay node comprising: aprocessor; and a communications subsystem, wherein the processor andcommunications subsystem cooperate to: receive parameters of a targetnetwork node from the source network node at the relay node; initiate adirect attachment of the relay node to the target network node; anddetach the relay node from the source network node.

The present disclosure further provides a method for managing a relaynode that is moving relative to a source network node, the methodcomprising: sending a handover request of a relay node from the sourcenetwork node to a target network node; performing handover of aplurality of user equipments (UEs) from the source network node to thetarget network node, wherein the plurality of UEs are attached to therelay node, and establishing an interface between the relay node and thetarget network node.

The present disclosure further provides a source network node configuredfor managing a relay node that is moving relative to the source networknode, the source network node comprising: a processor; and acommunications subsystem, wherein the processor and communicationssubsystem cooperate to: send a handover request of a relay node from thesource network node to a target network node; perform handover of aplurality of user equipments (UEs) from the source network node to thetarget network node, wherein the plurality of UEs are attached to therelay node, and establish an interface between the relay node and thetarget network node.

The present disclosure further provides a method for managing a relaynode that is moving relative to a source network node, the methodcomprising: selecting a lead node; connecting the plurality of relaynodes to the lead node; and transmitting a signal to manage mobility ofthe plurality of relay nodes from the lead node to a network node.

The present disclosure further provides a relay node configured to moverelative to a source network node, the relay node comprising: aprocessor; and a communications subsystem, wherein the processor andcommunications subsystem cooperate to: select a lead node; connect theplurality of relay nodes to the lead node; and transmit a signal tomanage mobility of the plurality of relay nodes from the lead node to anetwork node.

The embodiments of the present disclosure are provided with regard to3GPP LTE-Advanced. However, this is merely meant to be exemplary.Similar embodiments are possible with different types of networks andthe use of 3GPP LTE-Advanced is merely meant for illustration purposes.

In current 3GPP LTE-Advanced systems, various relay architectures havebeen proposed. These are described below as Architecture A, having threevariants, and Architecture B having a fourth variant.

References now made to FIG. 1, which shows Architecture A and thevarious alternatives in Architecture A.

In particular, in Architecture 100 of FIG. 1 a user UE 110 (also called“user-UE” in the following) communicates with a relay 120. In theembodiments of FIG. 1, relay 120 can be seen to be both an eNB to userUE 110 and as a UE to the remainder of the network architecture 100,shown by eNB 122 and UE 124 (also called “relay-UE” in the following).

Relay 120 communicates with DeNB function 130, which then communicateswith the relay-UEs serving gateway (S-GW) and packet data node (PDN)gateway (P-GW) 132. Depending on the implementation, DeNB function 130may also include relay-UEs serving gateway (S-GW) and packet data node(PDN) gateway (P-GW) 132 functionalities.

The DeNB function 130 also communicates with the relay-UE's mobilitymanagement entity (MME) 140.

The relay-UE's S-GW/P-GW 132 optionally communicates with a relaygateway 150 and with the user-UE's S-GW/P-GW 160. Further, therelay-UE's S-GW/P-GW 132 also communicates with user-UE's MME 170.

The alternative 1 to Architecture A, shown by box 180, the DeNB only hasthe eNB function (it does not function as S-GW/P-GW for the relay-UEs).The alternative 1, relay node is a “full L3 type relay”, whose S1interface and the signaling connections are routed through the DeNBtransparently.

In a third alternative, shown by box 184, the baseline solution of thealternative 1 is enhanced by integrating the S-GW/P-GW functionality forthe Relay-UEs (132) into the DeNB.

In a second alternative, shown by box 182, the DeNB is enhanced toinclude the functionality of the Donor eNB, the relay-UEs S-GW/P-GW 132and the relay gateway 150 S-GWP-GW. This results in the “Proxy S1/X2”architecture.

Each of all alternatives 1, 2 and 3 have their own characteristics. Thedifferent characteristics affect the underlying base RN procedures andin particular relate to how mobility how can occur for the RN. Thus,each architecture is more fully described below.

Alternative 1: Full-L3 Relay, Transparent for DeNB

Both the user plane (U-plane) and the control plane (C-plane) of the S1interface are terminated at the RN. U-plane packets of a user equipment(UE) served by the RN are delivered via the relays P-GW/S-GW and therelays radio bearers.

From a UE perspective, the relay is a serving eNB of the UE. The UEsS-GW/P-GW maps the incoming IP packets to the general packet radioservice (GPRS) tunneling protocol (GTP) corresponding to the evolvedpacket system (EPS) bearer of the UE and tunnels the packets to IPaddress of the RN. The tunneled packets are routed to the RN via therelay's P-GW/S-GW. EPS bearers of different UEs connected to the RN withsimilar quality of service (QoS) are mapped in one relay radio bearerover the Un interface.

References now made to FIG. 2, which shows the C-plane for thealternative 1.

As seen in FIG. 2, a UE 210 includes various layers, including physicallayer 212, PDCP, radio link control (RLC), medium access control (MAC)layer 214, radio resource control (RRC) layer 216 and non-access stratum(NAS) layer 218.

Relay 220 includes a split architecture with the left side being a eNBarchitecture and the right side being a UE architecture. In particular,relay 220 includes a physical layer 222 for both sides. Further, on theleft side of the control plane an RRC layer 224 is provided. On theright side of the control plane an internet protocol (IP) layer 225,Stream Control Transmission Protocol (SCTP) layer 226 and an S1Application Protocol (S1-AP) layer 227 are provided.

The relay communicates with a Donor eNB 230 which includes a split inthe control layers, with the left side towards the relay, and the rightside towards the relay's S-GW/P-GW. The left side includes a physicallayer 231, a PDCP/RLC/MAC layer 232. The right side has L1 layer 234, L2layer 235, IP layer 236, user datagram protocol (UDP) layer 237 and aGTP-u layer 238.

The S-GW/P-GW serving the relay layer 240 includes various layersincluding layer 1 242, layer 2 244, IP layers 245, UDP layer 246, GTP-Ulayer 247 and IP layers including the relay IP address point ofpresence, shown by layer 249.

Similarly, MME serving the UE 250 includes layer 1 252, layer 2 254, IPlayer 255, SCTP layer 256, S1-AP layer 257, and NAS layer 258.

Reference is now made to FIG. 3 which shows the user plane for the firstalternative. Similar to the control plane, the UE 310 communicates withrelay 320, Donor eNB 330, S-GW/P-GW serving the relay 340, and S-GW/P-GWserving the UE 350. Each of the layers in the control plane correspondswith its peer layer in the next end element.

Alt 2—Proxy S1/X2

In the second alternative, the U-plane of the S1 interface is terminatedat the RN and the DeNB. The S-GW serving the UE maps the incoming IPpackets to the GTP tunnels corresponding to the EPS bearer of the UE andsends the tunneling packets to the IP address of the DeNB. Upon the DeNBreceiving the tunneling packets from the S-GW, the received packets arede-tunneled and the user IP packets are mapped to another GTP tunnel andsent to the IP address of the RN.

EPS bearers of different UEs connected to the RN with similar QoS aremapped in one radio bearer over the Un interface.

Reference is now made to FIG. 4, which shows the control plane for thesecond alternative. In particular, UE 410 communicates with relay 420which communicates with Donor eNB 430 and MME 440. As seen in acomparison between FIG. 2 and FIG. 4, the embodiment of FIG. 4 does notinclude the S-GW/P-GW serving the relay since this functionality is nowpart of the Donor eNB.

Further, various layers correspond between the various elements in FIG.4.

Referring to FIG. 5, the user plane similarly shows that functionalitypreviously found in FIG. 3 has now been assumed by the Donor eNB. Inparticular, UE 510 communicates with relay 520 which communicates withDonor eNB 530 and the serving gateway (S-GW) 540.

Alt 3—RN Bearers Terminate in DeNB

In the third alternative, the baseline solution of Alt 1 is enhanced byintegrating the S-GW/P-GW functionality for the RN into the DeNB.Thereby, the routing path optimized as packets do not have to travelthrough a second P-GW/S-GW, but otherwise the same functionality andpacket handling as applied above with regard to alternative 1 isprovided.

Referring to FIG. 6, the C-plane architecture includes the UE 610, relay620, Donor eNB 630, S-GW/P-GW serving the relay 640 and MME serving theUE 650. In the alternative 3 shown in FIG. 6, the S-GW/P-GW 640 isintegrated into DeNB 630.

Further, in this architecture, referring to FIG. 7, the U-plane of theS1 interface is terminated at the RN. The S-GW serving the UE maps theincoming IP packets to the GTP tunnels corresponding to the EPS bearerof the UE and sends the tunneled packets to the IP address of the RN.The DeNB is simply acting as an IP router in the example of architecture3 and forwards the GTP-U/UDP/IP packets between two interfaces. The DeNBperforms this router functionality via the P-GW like functionality inthe DeNB.

Referring to FIG. 7, UE 710 communicates with relay 720 whichcommunicates with Donor eNB 730 which communicates with S-GW/P-GW 740.Thus, the relay 720 may communicate directly with S-GW/P-GW 740 in theembodiment of FIG. 7.

The DeNB also performs other P-GW like functionality for the UE side ofthe relay such as the management of QoS. EPS bearers of different UEsconnected to the RN with similar QoS are mapped in one radio bearer overthe UN interface.

Alt 4—S1 UP Termination in DeNB

As indicated above, a second architecture, labeled as architecture B hasa fourth alternative which is the S1 user plane (UP) is terminated atthe DeNB. The S-GW serving the UE maps the incoming IP packets to theGTP tunnels corresponding to the EPS bearer of the UE and sends thetunnelled packets to the IP address of the DeNB. Upon the DeNB receivingthe tunneled packets from S-GW, the received packets are de-tunnelledand the inner user IP packets are mapped to the Un radio bearerscorresponding to the EPS bearer of the UE. Each EPS bearer of the UEconnected to the RN is mapped to separate radio bearers over the Uninterface.

Specifically referring to FIG. 8, FIG. 8 shows the control plane for thefourth alternative in which UE 810 communicates with relay 820, DonoreNB 830, and MME serving the UE 840.

Similarly in FIG. 9, the user plane is shown for UE 910, relay 920,Donor eNB 930 and S-GW/P-GW serving the UE 940.

With regard to the above four alternatives, the assumption is that theRN is stationary. Hence the above described architectures are designedbased on stationary relays and do not directly apply to a scenariohaving a moving RN. However, when the RN is mobile, not only does the RNneed to be handed over to another cell, but also the UEs connected tothe RN cell will also be impacted. For a moving RN, the embodimentsdescribed herein enable mobile relays to be handed to other cells andminimize QoS impact to UEs actively connected to the RN.

For example, one embodiment that utilizes a mobile relay would be in afast moving vehicle. The mobile relay is deployed to improve the qualityof service for UEs on that vehicle. In order to achieve the improvedquality of service, mobile relay handover reliability should be high andhandover latency should be reduced as much as possible. Otherwise, allUEs connected to the mobile relay would lose network connections as aresult of RN handover failure.

In the embodiments described below, the second alternative architectureis generally used as an example. However, the other alternatives arealso considered for purpose of supporting mobile relays. Possibleenhancements to improve a RN handover reliability and latency are alsoprovided below.

RN Mobility—Alternative 2

X2-Based RN Mobility Procedures.

From the above alternatives, alternative 2 is provided as an example ofa relay architecture for LTE-A. In this architecture, the user plane(U-plane), and the control plane (C-plane) of the S1 connections bothterminate at the RN. The designated eNB serves as a proxy for the RNcell with the relay gateway functionality. The designated eNB proxyswitches the general packet radio service (GPRS) tunneling protocol(GTP) tunnels spanning from the S-GW/P-GW of the UE to the DeNB toanother GTP tunnel going from the DeNB to the RN. There is a one to onemapping between the two GTP tunnels.

On the control plane, with the DeNB proxy functionality, the S1-APmessages sent between the MME and the DeNB are translated into S1-APmessages between the DeNB and the RN by modifying the S1-AP UE IDs inthe message and leaving other parts of the message unchanged.

In one embodiment, the DeNB S1-AP proxy operation is transparent for theMME and the RN. In other words, from the MME's perspective, only theDeNB is seen and the UE connects to the DeNB directly. From the RN'sperspective, it is not aware of the DeNB proxy operation and thus thecommunications are as if the RN talks to the MME directly. Therefore,when the RN moves from one DeNB to another DeNB, the MME which servesUEs under the RN cell would need to switch the UEs GTP tunnel end pointto the target eNB. In addition, the RN cell UE contexts may need to beforwarded from the source eNB to the target eNB so that the target DeNBcould operate as the proxy S1/X2 for UEs handed over along with the RN.

From a UE's perspective, the UE is not aware of the RN handover as it isconnected to the same serving cell (i.e., RN) during the process. It isthe source DeNB's responsibility to inform the target DeNB about the RNcell UE contexts and also initiate group mobility procedures on behalfof the RN cell UEs. It is also possible that the RN informs the targetDeNB about RN cell UE contexts.

For RN mobility procedure, the process for RN mobility and theassociated UE mobility can be characterized by 3 steps. In a first step,the RN is handed over from the source DeNB to the target DeNB. In asecond step, the S1/X2 interface is established between the RN and thetarget DeNB. In a third step, the UEs under the RN cell are handed overas a result of RN mobility.

In one embodiment, the second and third steps above may be handled inparallel as an optimization to minimize UE handover latency. Further,although detailed operation of each step among different architecturesvaries, the general 3 step procedure typically applies to any relayarchitecture.

Reference is now made to FIG. 10. In FIG. 10 UE 1010 communicates withRN 1012. Further, DeNB 1014 is the source DeNB for RN 1012. DeNB 1016 isthe target DeNB for RN 1012 during mobility. MME 1018 is the MMEresponsible for RN 1012. Further, S-GW/P-GW 1020 for UE 1010 maycommunicate with the various DeNBs.

In the embodiment of FIG. 10, the RN is moving towards a cell edge ofsource DeNB 1014 and needs to be transitioned to target DeNB 1016. Thus,in accordance with the first step described above, the RN is handed overfrom the source DeNB to the target DeNB. This is illustrated by box1022.

As a first step of the RN mobility process, the RN is handed over fromthe source DeNB to the target DeNB by acting as a UE. Success of RNhandover as a UE from one DeNB to another DeNB is needed in order tocontinue to serve the UEs under the RN cell. Since the RN acts as a UE,the LTE handover procedures may be utilized. In particular, the RN 1012sends a measurement report 1030 to source DeNB 1014. The source DeNBmakes a handover decision based on the measurement report 1030 andselects a target cell.

The source DeNB 1014 then sends a handover request message to the targetDeNB 1016 over an X2 interface, is shown by arrow 1032.

The target DeNB 1016 receives the message and responds with a handoverrequest acknowledgement message over the X2 interface, as shown by arrow1034.

The source DeNB 1014 receives the acknowledgement message and send ahandover command message to RN 1012, shown byRRCConnectionReconfiguration message 1036. If there is any RN bearerpackets not sent at the source DeNB, those packets can be forwarded tothe target DeNB as shown by arrow 1038. Source DeNB 1014 also provides asequence number (SN) status transfer over the X2 interface, as shown byarrow 1040.

The RN 1012 receives the handover command message, attaches to thetarget DeNB and completes its handover process. This is shown by theRRCConnectionReconfigurationComplete message shown at arrow 1042.

After the completion of the RN handover, the MME 1018 which serves theRN switches the GTP tunnel endpoint corresponding to the RN bearers tothe target DeNB, as shown by arrow 1044.

Upon the RN path switch, target DeNB 1016 then sends an RN ContextRelease message to source DeNB 1014, as shown by arrow 1046.

Although the step 1 procedures is shown by box 1022 are generally thesame as the procedure for UE handover in LTE, modification toinformation elements of the HANDOVER REQUEST and HANDOVER REQUESTACKNOWLEDGEMENT messages 1032 and 1034 respectively are made in oneembodiment to indicate that handover is for a relay node and tocharacterize the RN radio bearer or the UE under the RN cell bearerinformation.

For example, LTE released 10 handover request messages contain UEcontext information, including a list of UE bearers and associatedquality of service parameters.

If the same information elements are used for RN handover requestmessages, then the information elements may contain the RN contextinformation including the list of RN bearers and associated QoSparameters.

However, using an existing HANDOVER REQUEST message may not beappropriate for an RN for the following reasons. First, in currenthandover request messages there is no information element indicating ifthe request is from a UE or an RN. However, under the second alternativearchitecture, if the target eNB does not have proxy functionality itshould not accept a handover request since it will be unable toaccommodate the proxy functionality for the RN.

Presently a target DeNB's proxy capability may not be known to thesource eNB through X2-AP messaging. Thus, in one embodiment anindication may be provided in a HANDOVER REQUEST message to indicate thehandover request message is for the RN in order for it to allow thetarget eNB to make a proper handover decision.

Secondly, since the DeNB serves as a proxy node for the RN, there is noRN bearer in the architecture carrying a UE's traffic. Only the RN radiobearer from the DeNB to the RN carries the UE data. The target eNB wouldnot be able to evaluate if it has sufficient radio resources to servethe RN based on a current handover request message, for example.

In order to address the above issues, various options are possible.First, to select an eligible target DeNB having the capability tosupport the RN, various solutions are possible. In a first solution, anadditional information element may be added to a handover requestmessage as a relay node indicator such that the target eNB candifferentiate handover requests for UEs and handover requests for RNs,and respond accordingly. Such an information element could, for example,be as small as one bit to flag to indicate whether the request is for aUE or an RN. Multi-bits flag are also possible to indicate additionalinformation.

A second option to select eligible target DeNBs with RN supportcapabilities is to exchange RN proxy capabilities among neighboring eNBsso that neighboring eNBs are aware in advance of the capabilities of theneighbors. In this way, the HANDOVER REQUEST message does not need toindicate a node type since the source DeNB only sends the handoverrequest message to eNBs that have RN proxy capabilities. The exchange ofinformation may occur, in some embodiments, utilizing signaling over theX2 interface.

In a third option, the RN itself could perform neighbor cellmeasurements, similar to UEs that utilize the LTE 3GPP standards. Thus,the RN may limit it's measurements to only certain cells which have theproxy X2/S1 functionality to support a type 1 relay. For example,neighboring eNBs may exchange their capability to support X2/S1 proxyfunctionality by X2 signaling. The eNBs may indicate the proxycapability of neighbor cells by including the eNB capability in their RNspecific information. This information may be included in messages, suchas the RN Reconfiguration message, as defined by the 3GPP standards.

The RN may read the RN specific information and limit its neighbor cellmeasurements to only those cells which support proxy capabilities andreport the measurements back to the serving cells. The measurementreports may be included in an RN specific RRC message, for example.

In a fourth option for determining the capabilities of a target eNB, theenhanced universal terrestrial radio access network (E-UTRAN) providesmeasurement configurations applicable for the RN through dedicatedsignaling. For example, the E-UTRAN may utilize theRRCConnectionReconfiguration message. Similar to regular UEs, themeasurement procedures distinguish between various types of cells. Theseinclude the serving cell, listed cells and detected cells. The DeNB canuse the “CellsToRemoveList”, the “CellsToAddModList” fields in the“MeasObjectEUTRA” to direct the RN to perform measurement towardpotential target DeNBs that have the capability to serve the RN. The MMEof the RN could provide a list of potential target DeNBs that the RN canmove to.

In a fifth option for determining the capabilities of target eNBs, theRN may signal its requirement for a proxy enabled target eNB. Forexample, the RRCConnectionReconfigurationComplete message sent from theRN to the target DeNB may include an indication that the message wassent from an RN as opposed to a UE. If the target DeNB does not haveproxy functionality, the target DeNB could release the RRC connectionwith the RN or direct the RN to another cell.

In a sixth option for discovering the capabilities of the target DeNB,the RN context within the source eNB contains information regardingroaming restrictions that were provided either at connectionestablishment or at the last tracking area update. The RN can perform atracking area update (TAU) with the MME, and the MME could inform theDeNB of a list of eNBs that have RN proxy capability. Accordingly, theDeNB could perform a handover request to eligible eNBs that can supportRN functionality. The tracking area update can be performed regularly,for example using a timer, or may be triggered by an event such as ahandover, for example.

A second consideration for the steps in a box 1022 is the issue ofwhether target eNB has enough resources to serve the RN based on aHANDOVER REQUEST message. In one embodiment, therefore, the RN mayprovide the RN/UE bearer information in a HANDOVER REQUEST message for atarget DeNB to allow the target DeNB to make proper handover decisions.Various options are possible for providing such information.

In a first option, the normal Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) Radio Access Bearer (E-RAB) information may bereplaced with radio bearer information in the handover request messageif a RN is being handed over. If the handover request is for an RN, the“E-RABs To Be Setup List” information element (IE) associated with theRN includes the RN radio bearer ID (instead of “E-RAB ID”) and qualityof service parameters of the RN radio bearers (instead of “E-RAB LevelQoS Parameters”), which is contained in the handover request message.The target eNB can decide whether to accept or reject the RN radiobearer based on the information provided.

Corresponding to the modifications made to the handover request message,in the HANDOVER REQUEST ACKNOWLEDGEMENT message, the admitted and/or notadmitted RN radio bearer list is provided under “E-RABs Admitted List”and “E-RABs Not Admitted List”. If the admission control of the targetDeNB accepts the RN, a dedicated random access channel (RACH) preamblemay be provided so that the RN can perform non-contention-based randomaccess towards the target DeNB.

In a second option for providing information, per UE bearer informationcan also be included in the RN handover request message instead of theRN bearer information. As the source DeNB is the proxy node and hasaccess to all the UE bearers, the UE context information can be includedinstead. That is, a per UE radio access bearer to be set up list,including the E-RAB ID, E-RAB level QoS parameters, uplink GTP tunnelpoint, among other information, may be included in the handover requestmessage. Based on the per UE bearer information, the target DeNB couldaccept or reject the handover request.

Correspondingly, the admitted and/or not admitted per UE E-RAB listcould be provided in the handover request acknowledgement message. Ifthe admission control of the target DeNB accepts the RN, a dedicatedRACH preamble may be provided so that the RN can performnon-contention-based random access toward the target DeNB. The handoverrequest acknowledgement message may also include the uplink and downlinkGTP tunnel information for the admitted E-RABs.

Referring again to FIG. 10, a second step shown by box 1050, establishesthe S1/X2 between the RN and target DeNB.

After the RN attaches to the target DeNB, the RN establishes the S1/X2interface with target DeNB 1016. The previous S1/X2 connection withsource DeNB 1014 is then terminated. Such establishment may require thatexisting S1/X2 connections of these target DeNB 1016 need to be updated.For example, the S1/X2 interface may need to register the new cell ofthe RN toward neighbor eNBs of the DeNB or to register new tracking areacodes (TAC) corresponding to the RNs cell toward the MME 1018. Theexisting eNB configuration update procedures on the S1/X2 interfaces maybe used for this purpose in one embodiment.

Target DeNB 1016 may initiate an “eNB Configuration Update” procedure tothe UE's MME and also to neighboring eNBs. After the S1/X2 connectivitywith the target DeNBs established, the RN is ready to operate as anetwork node and continues serving the UEs under its cell. Thus, in FIG.10, as shown by arrow 1052, the setup of the S1 interface is performed.

Further, as shown by arrow 1054, the setup of the X2 interface isperformed between RN 1012 and target DeNB 1016.

Further, target eNB 1016 sends an eNB configuration update message tosource DeNB 1014, as shown by arrow 1056 and source DeNB 1014 sends anacknowledgement back to target DeNB 1016, as shown by arrow 1058.

In one embodiment, no modifications to existing S1/X2 messages are madeduring the steps at box 1050.

The third step for handover of an RN is to handover the UEs under the RNcontrol. This step is shown with regard to box 1060 in the embodiment ofFIG. 10. Although the UEs are connected with to same serving cell andare not involved in handover process in the second alternativearchitecture, from the MME's perspective, the UE serving cell is changedfrom the source DeNB 1014 to the target DeNB 1016. Further, the UEcontexts need to be transferred from source DeNB 1014 to target DeNB1016 for target DeNB 1016 to operate as a proxy for the RN cell UEs.

Thus, in box 1060, the source DeNB 1014 sends a handover request messageon behalf of the UEs to target DeNB 1016. This is shown by arrow 1062.The sending of the handover request is done even though the UEs have notinitiated any handover request. Existing handover request messages canbe used by handling each UE handover request individually.

Similarly, a path switch message can be handled on a per individual UEbasis. Such messages are generally sent over a backhaul link.

Existing handover procedures have handover requests that are generallyinitiated after the eNB has received a measurement report from a UE.However, with a RN, the handover message for the UE is sent from sourceDeNB 1014 to target DeNB 1016 without receiving any measurement reportfrom the UE to initiate the UE handover process. The source DeNB canaccess the UE bearer and is able to initiate UE handover processes afterreceiving the measurement report from the RN.

Further, in existing handover procedures, after receiving a handovercommand message, the UE will access the target cell using a randomaccess channel (RACH) procedure. However, in the embodiment of FIG. 10,the UE is not involved in the handover process over the Uu interface,and the target cell will not receive anyRRCConnectionReconfigurationComplete message from the UE. Thus,differing from the existing UE handover procedures, the target DeNB 1016will request path switch without receiving theRRCConnectionReconfigurationComplete message from the UE.

Referring again to FIG. 10, as a result of receiving the handoverrequest message from source DeNB 1014, target DeNB 1016 sends a handoverrequest acknowledgement message, shown by arrow 1064.

Further, the target DeNB 1016 then initiates the UE path switch with theS-GW/P-GW 1020, as shown by arrow 1066.

The source DeNB 1014 forwards packets to target DeNB 1016, as shown byarrow 1068.

Once the path switch has occurred, source DeNB 1014 sends a SN statustransfer message, as shown by arrow 1070, to target DeNB 1016. TargetDeNB 1016 then sends a UE context release message, as shown by arrow1072, to the source DeNB 1014.

In accordance with the embodiment of FIG. 10, no handover commandmessages are sent from the RN to the UE. The UE mobility procedure istransparent to the UEs under the second architecture RN cell.

Overall, the steps show by box 1060 enable UE mobility as a result of RNhandover. After the completion of the messages in block 1060, RNhandover and UE mobility procedures are completed.

Further, the messages of box 1060 may be handled in parallel with thoseof box 1050.

Further, if UE context information is included in message 1032, the UEhandover request and handover request acknowledgement messages may beomitted from the steps of box 1060. Further, UE context transfer canstart after the source DeNB 1014 has received the handover requestacknowledgement message 1034. Thus, the messages of box 1060 can bemerged with those of box 1022 if per UE bearer information is includedin the RN handover request message. This simplifies the RN mobilityprocedure and reduces the handover latency for UEs. Otherwise, themessages of bock 1060 are processed after RN handover is completed andseparate handover request messages are needed for each UE.

In another possible alternative, at the end of the messages of box 1022,the handover complete message sent from the RN to the target DeNB couldinclude all UE contexts to send to the target DeNB. The target DeNB 1016may request a path switch for all the UEs that were provided in themessage.

S1-Based RN Mobility Procedure

The procedure described above with regard to FIG. 10 is X2 based, whichrelies on information exchanged between the source DeNB 1014 and targetDeNB 1016 through the X2 interface. However, in E-UTRAN, inter-cellhandover may be initiated by the S1 interface when X2 based handover isnot available. This may occur, for example, when there is no X2interface between the source and target eNBs or when the MME needs to bechanged.

The S1 based handover procedure relies on the MME to transfer handovermessages between the source eNB and the target eNB. Similar proceduresto those described above with regard to FIG. 10 may be implementedutilizing an S1 based RN handover.

Reference is now made to FIG. 11 which shows a UE 1110, RN 1112, sourceDeNB 1114, target DeNB 1116 MME for the RN 1118 and MME for the UE 1120and an S-GW/P-GW for the UE 1121. In the embodiment of FIG. 12, thesource DeNB 1114 and target DeNB 1116 do not have an X2 interfacebetween them.

The first step of the handover procedure is shown by the box 1122 inFIG. 11. In this case RN 1112 sends a measurement report, shown by arrow1130, to source DeNB 1114. The source DeNB 1114 then indicates thathandover is required in a message 1132 between the source DeNB 1114 andthe MME 1118.

The MME 1118 then sends a handover request, shown by arrow 1134 totarget DeNB 1116 and target DeNB 1116 then sends a handover requestacknowledgement, as shown by references numeral 1136. The message atarrow 1136 is sent to MME 1118.

As a result of the receipt of the message at arrow 1136, MME 1118 sendsa handover command back to source DeNB 1114, as shown by arrow 1138. Thesource DeNB 1114 then sends an RRCConnectionReconfiguration message, asshown by arrow 1140, to RN 1112.

Source DeNB 1114 then sends an eNB Status Transfer message to MME 1118,as shown by arrow 1142 and the MME 1118 sends an MME Status Transfermessage, as shown by arrow 1144 to target DeNB 1116.

The RN 1112 then sends an RRCConnectionReconfigurationComplete messageto the target DeNB 1116, as shown by arrow 1146 and target DeNB 1116performs an RN path switch, as shown by arrow 1148.

Thus, according to FIG. 11, the Handover Required message 1132 theHandover Command message 1138 and the eNB Status Transfer message 1142are sent utilizing the S1 interface.

Further, the handover request message 1134, handover requestacknowledgement 1136 and MME status transfer 1144 messages are also sentbetween MME 1118 and target DeNB 1116 using the S1 interface. Asindicated above, the RN MME may not know the target eNB's RN supportcapabilities. An RN indication can be added in the S1 handover requestmessage to indicate to the target eNB about RN handover. The target eNBcan accept or reject the handover based on its RN support capability.Alternatively, in the S1 setup message, an RN support indicator can beadded to indicate the eNB's RN support capability to the MME. If the RNsupport indicator is added to the S1 setup message, the RN MME will onlysend the handover request message to the target DeNB 1116 if that targetDeNB has the capability to support the RN.

Existing signaling messages may need to be modified in order to supportRN mobility and include the handover request 1134, the handover requestacknowledgement 1136 or the RRC connection reconfiguration completemessage 1146.

After the RN is handed over from the source DeNB to the target DeNB,similar procedures as described above with regard to the X2 based RNmobility are performed by the RN to establish the S1 and X2 interfaceswith the target DeNB. In particular, referring to FIG. 11, box 1150shows the setup between RN 1112 and target DeNB 1116 of the S1interface, shown by arrow 1152 and also the setup of the X2 interfacebetween these two entities, as shown by arrow 1154.

Further, the target DeNB sends an eNB configuration update to the UE MME1120, as shown by arrow 1156 and an eNB configuration updateacknowledgement is sent back from MME 1120 to target DeNB 1116, as shownby arrow 1158.

Finally, S1 based UE under the RN cell context transfer is performed inorder for the target DeNB 1116 to operate as a proxy for the RN cellUEs. This is shown by the messages in block 1160. In particular, sourceDeNB 1114 sends a handover required message for the UE over the S1interface to the MME 1120, as shown by arrow 1162. The MME 1120 thensends a handover request to target DeNB 1116, as shown by arrow 1164.The DeNB 1116 then sends a handover request acknowledgement as shown byarrow 1166 to the MME 1120.

MME 1120 then sends a handover command to source DeNB 1114 over the S1interface, as shown by arrow 1168 and the source DeNB 1114 then sends aneNB status transfer message over the S1 interface, as shown by arrow1170.

MME 1120 then sends an MME status transfer over the S1 interface totarget DeNB 1116, as shown by arrow 1172. The target DeNB 1116 and MME1120 then perform a UE path switch, as shown by arrow 1174.

Thus, based on the above, the handover in the second architecture can beperformed over either the X2 or the S1 interfaces.

RN Handover Failure Procedure

In both the X2 based RN handover of FIG. 10 in the S1 based RN handoverof FIG. 11, there is a chance that the RN may experience handoverfailure due to a rapid change of radio conditions. Both the source DeNBand the RN keep some context, for example the Cell Radio NetworkTemporary Identifier (C-RNTI), to enable the return of the RN in thecase of handover failure.

When the RN detects radio link failure during the handover process theRN proceeds through a radio link recovery process similar to a UE toattempt to attach to a DeNB. The handover process failure may, forexample, result from a RACH procedure toward the target DeNB not beingsuccessful within a certain time.

Upon detecting radio link failure, the RN discards any current RNsubframe configuration, enabling the RN to perform normalcontention-based RACH as part of the re-establishment. Upon successfulre-establishment, the RN subframe configuration can be configured againusing the RN configuration procedure. If the radio link cannot berecovered within a certain duration, the RN will go into an RRC idlestage and reinitiate its RRC connection to an appropriate DeNB. This issimilar to the RN startup procedure shown with regard to FIG. 12.

In particular, referring to FIG. 12 RN 1210 communicates with a donoreNB 1212. Further, MME 1214 is in communication with RN 1210 and withDeNB 1212.

Home Subscriber Server HSS 1216 further communicates with a MME 1214.

Operations & Maintenance (O&M) system 1218 further communicates with RN1210.

In a first step, RRC setup occurs, as shown by block 1220. This occursbetween RN 1210 and donor eNB 1212.

The RN 1210 then performs a UE attach procedures, as shown by arrow 1222with MME 1214 which then obtains subscription data from HSS 1216, asshown by arrow 1224.

Donor eNB 1212 then creates a default bearer as shown with MME 1214, asshown by arrow 1226 and then UE context setup occurs between DeNB 1212and MME 1214, as shown by arrow 1228.

RRC reconfiguration then occurs between RN 1210 and DeNB 1212, as shownby arrow 1230.

After this point, user plane IP connectivity exists between RN 1210 andDeNB 1212.

The RN then performs node configuration download from the O&M system1218, as shown by arrow 1240.

The RN then sets up an S1 interface with DeNB 1212, as shown by arrow1242 and the X2 interface setup is shown by arrow 1244. For both S1 andX2, the DeNB 1212 performs eNB configuration updates, as shown by arrow1246 and 1248.

The embodiment of FIG. 12 therefore shows the setup of the RN with thenetwork from an RRC_IDLE state.

RN Mobility Procedure with Alternative 1

Reference is now made to FIG. 13. In FIG. 13 UE 1310 communicates with arelay 1312, which communicates with a source DeNB 1314, target DeNB1316, the relay MME 1318, and the relay SWG/PWG 1320.

The transfer in accordance with the alternative 1 requires the relay1312 to send a measurement report message, as shown by arrow 1330 tosource DeNB 1314. Source DeNB then makes a handover decision and sends ahandover request to target DeNB 1316 as shown by arrow 1332. The targetDeNB 1316 sends a handover request acknowledgement back source DeNB1314, as shown by arrow 1334.

As a result of the acknowledgement, source DeNB 1314 sends an RRCconnection reconfiguration message to RN 1312, as shown by arrow 1336.

The source DeNB 1314 then sends an SN status transfer message to targetDeNB 1316, as shown by arrow 1340. Relay 1312 sends a RRC connectionreconfiguration complete message 1342 to target DeNB 1316, which thenperforms a path switch request with the relay MME 1318, as shown byarrow 1344.

MME 1318 then sends the user plane update request, shown at arrow 1346,to the relay S-GW/P-GW 1320.

As a result of the message, the user plane update response is sent fromrelay S-GW/P-GW 1320 to the relay MME 1318, as shown by arrow 1350. Apath switch request acknowledgement is then sent from MME 1318 to targetDeNB 1316, as shown by arrow 1352 and a UE context release message isthen sent to source DeNB 1314, as shown by arrow 1354.

Thus, in the alternative 1, the handover from the source DeNB to thetarget DeNB is similar to the messages of box 1022 from FIG. 10.

In the alternative 1, the RN-P-GW maps the UE bearer to corresponding RNbearers and encapsulates the RN bearer packets to an outer RN GTP tunnelwhich ends at the DeNB. Since the RN is transparent to the DeNB, theDeNB cannot access the UE bearer and will not initiate the UE mobilityprocedure. From a UE-MME point of view, the UE under the RN cell staysin the same serving cell and there is no change of operation due to theRN handover.

The RN P-GW is informed of the RN handover and will route the RN bearerpackets to the target DeNB as a result of the RN handover. The S1interface between the RN and UE MME is not impacted because of the RNhandover. The X2 interface between the RN source DeNB should be removedafter the RN handover, a new X2 interface between the RN and target DeNBshould be established. This may require that the existing S1/X2connections of the DeNB are updated, for example, to register the newcells of the RN towards to the neighbor eNBs of the DeNB or to registernew tracking area codes corresponding to the RN cells towards the MME.Existing eNB configuration update procedures on the S1/X2 interfaces canbe used for this purpose.

Thus, in accordance with the embodiment for the first architecture, whenthe RN changes its DeNB during handover, there is no impact on the Uuradio bearer of the UE as well as the external bearer of the RN betweenthe RN-P-GW and UE-MME. The RN mobility can be supported through thehandover procedures for the alternative 1 and no additional elements areadded to for the UE mobility. However, supportive RN operation is neededat the target DeNB. Therefore, the RN may need to indicate its node typein the handover request message. If the target DeNB cannot support RNnode operation, the target DeNB may reject the RNs handover request. Ifneighboring eNBs exchange the RN proxy capability in advance, then anindication may not be needed.

While the above is described with regard to X2 communications betweenthe source DeNB and Target DeNB, similar procedures could also beimplement utilizing the S1 interface.

RN Mobility Procedure with the Third Alternative Architecture

In a third alternative architecture, the RN-P-GW is located at the DeNBto avoid packets routing with the second P-GW/S-GW before arriving atthe DeNB. Reference is now made to FIG. 14, which shows UE 1410, RN1412, source DeNB 1414, target DeNB 1416, MME 1418, MME for the UE 1420and S-GW/P-GW 1422.

Similar to the alternative 1, the RN mobility process is transparent tothe UEs and there are no impacts on the Uu radio bearer of the UE.Existing signaling messages may need to be modified in order to supportRN mobility.

In particular, RN 1412 sends a measurement report to source DeNB 1414,as shown by arrow 1430. The source DeNB 1414 then sends a handoverrequest 1432 to target DeNB 1416. This handover request may need to bemodified for RN mobility.

Target DeNB 1416 then sends a handover request acknowledgement 1434which may also may need to be modified based on the RN mobilityscenario.

As a result of the acknowledgement, source DeNB 1414 sends an RRCconnection reconfiguration message to RN 1412, as shown by arrow 1436.

RN bearer packet forwarding occurs between the source DeNB 1414 andtarget DeNB 1416, as shown by arrow 1438. Further, an SN status transfermessage is also sent between source DeNB 1414 and target DeNB 1416, asshown by arrow 1440.

The RN 1412 then sends an RRC connection reconfiguration completemessage, shown by arrow 1442. An RN path switch then occurs for thetarget DeNB and RN MME 1418, as shown by arrow 1444 and the RN contextrelease is then sent between target DeNB 1416 and source DeNB 1414, asshown by arrow 1446.

In accordance with the embodiment of FIG. 14, the S1 interface is thenset up between the RN and the UE MME 1420, shown by arrow 1460 and theX2 interface is set up between RN 1412 and target DeNB 1416, as shown byarrow 1462. Target DeNB then sends an eNB configuration update to sourceDeNB 1414, as shown by arrow 1464 and the eNB configuration updateacknowledgement is sent back to target DeNB, as shown by arrow 1466.

Since the RN-P-GW functionality is located at the target eNB 1416 inorder to support the RN, the RN should indicate its node type in thehandover request message, similar to the alternative 2 example above.eNBs that do not have RN S-GW/P-GW functionality may reject the handoverrequest correspondingly. Further, if neighboring eNBs exchange RN proxycapability in advance, this indication may not be needed.

When the RN is handed over to the target DeNB, the RN P-GW/S-GW movesfrom the source DeNB to the target DeNB consequently. From the UE MMEpoint of view, the RN has changed the IP address and the S1 bearer ofthe UE and should be re-established. To resolve this issue, the RN mayre-establish its S1 connection with all UE MMEs so that the UE MMEs willroute the UE packets to the target DeNB. The S1 bearer re-establishmentwith the MMEs may take a long time. However, in certain scenarios suchas the mobile relay for a high speed train, this S1 interface may bepreconfigured for the RN since the movement and handover may bepredetermined. Such optimizations are described below in more detail.

Similarly, the X2 interfaces of RNs may need to be re-established as theRN P-GW/S-GW changes IP addresses. Further, the existing S1/X2connections of the DeNB may need to be updated. Existing eNBconfiguration update procedures on the S1 X2 interfaces may be used forthis purpose.

After the S1 interfaces are re-established with UE MMEs, the UE packetsmay be routed to the target DeNB without additional signaling exchangedover the backhaul. Thus, from FIG. 14, the RN mobility procedure onlyuses the step 1 and step 2 procedures from the second alternativearchitecture.

The RN mobility procedure in the third alternative is similar to thealternative 1. Modifications may be needed to current procedures toinclude relay node indications in the handover message. In addition, theRN would need to re-establish the S1/X2 interface to go into normalnetwork operation after being handed over.

RN Mobility Procedures with the Fourth Alternative Architecture

In the fourth alternative architecture, the DeNB acts as a terminationfor the S1 connection towards the EPC and the RN can simply be seen as acell managed by the DeNB from the EPC and neighboring eNB's point ofview. The DeNB acts as an S1-AP gateway, similar to the Home eNB (HeNB)gateway. Thus, the main difference between the fourth alternative andthe second alternative is in the S1 user plane, where the GTP tunnel forthe UE bearer ends at the DeNB and node GTP tunnel for the RN/UE bearerexists between the DeNB and RN in the fourth alternative.

The mobility procedure here is the same is that described above withregard to FIG. 10, where the RN is handed over as a UE first and thenthe handover for UEs under RN cell mobility procedures are triggered.

The modifications to existing procedures for the fourth alternative arethat the relay node indication in the Handover Request message isprovided. Further, the UE context information may be included in the RNhandover message. Otherwise the UE mobility procedure may be triggeredas in the block 1060 of FIG. 10.

Further, the target DeNB may request UE path switch after the RN isattached to the target DeNB without receiving a UE RRC connectionreconfiguration complete message. No handover command is sent to the UEin the present embodiment.

Further Enhancements for RN Mobility

The above embodiments describe situations in which the RN can be mobileand serve UEs under its cell and an LTE network. In some embodiments, itis possible to reduce the amount of time that such handover takes. Theembodiments below describe several enhancements that may be implementedwith the above techniques. In all of the embodiments below, aspects fromthe above embodiments may be used in conjunction with the embodimentsbelow. Further, the embodiments below may be used together in somecases.

Step 1 Enhancements

All of the above embodiments have the handover of the RN from the sourceDeNB to the target DeNB as a UE. In some embodiments, choosing anappropriate handover parameters, such as smaller handover thresholds andshorter time-to-trigger (TTT) for measurement reports, may aid intriggering handover earlier in a high speed environment and thus reducethe handover failure rate.

In an alternative 1 embodiment, a fast handover command may be utilized.For example, in a relay situation where the relays are part of publictransportation such as a high speed train, the high speed scenario poseschallenges to RN mobility due to the frequent handovers and fastchanging radio conditions. On the other hand, various characteristics ofthe high speed train scenario can be taken advantage of to improve userexperience.

One feature of a high speed train application is that many eNBs areplaced on the route of the high speed train for the purpose of servingthe train, especially in rural areas that the train passes by. There islittle or no traffic for these eNBs before or after the train arrives orleaves the area. When the RN is handing over to these eNBs, the targeteNBs are almost always available with full radio resources. Thus, thetraditional network controlled UE assisted handover procedures can beoptimized in such scenarios. The present disclosure is not however meantto be limited to high speed train scenarios and other similar scenariosfor transport can be used, including relays on buses traveling onhighway networks, aircraft using specific flight patterns among others.

In accordance with one alternative embodiment, one optimization is tohave the handover command from the source DeNB to the RN sent beforereceiving a handover request acknowledgement message from the targetDeNB. Reference is now made to FIG. 15. In FIG. 15 UE 1510 communicateswith RN 1512. Further communication occurs between various ones of thesource DeNB 1514, target DeNB 1516, MME 1518 and SWG/PWG 1520.

As seen in embodiment of FIG. 15, the RN sends a measurement report tosource DeNB 1514, as shown by arrow 1522.

As seen in the embodiment of FIG. 15, source DeNB 1514 sends a handoverrequest, shown by arrow 1530, to target DeNB 1516.

Before the handover request acknowledgement message, shown by arrow1532, is received from target DeNB 1516, source DeNB 1514 then sends theRRC connection reconfiguration message to RN 1512, as shown by arrow1540. The sending of the message at arrow 1540 prior to the receiving ofthe handover request acknowledgement 1532 speeds the handover process,and in rapidly changing radio conditions has a higher chance of successto actually trigger the handover at RN 1512.

RN 1512 then sends an RRC connection reconfiguration complete message totarget DeNB 1516, as shown by arrow 1542 and the remaining steps of thefirst step in the transition proceed as previously described. Namely,packet forwarding occurs, as shown at arrow 1550, the RN path switch isperformed between target DeNB 1516 and MME 1518, shown by arrow 1552,the SN status transfer message is sent from source DeNB 1514 to targetDeNB 1516, shown by arrow 1554, and the target DeNB 1516 sends an RNcontext release message to source DeNB 1514, shown by arrow 1556.

For the above, to facilitate RN handover, the C-RNTI and one or morededicated RACH preambles can be pre-allocated for RN handover. This maybe done, for example, through X2 interface negotiations between theDeNBs or through an initial pre-configuration.

Alternatively, when the mobile RN first connects with the source DeNB,the source DeNB may start a handover preparation procedure with possibleneighboring DeNBs. The possible target DeNBs then allocate the C-RNTIand the dedicated RACH preambles for the potential coming RN handover.

Further, the possible target DeNBs may prepare the radio resource. Thetarget DeNB 1516 radio resource information and security configurationmay be forwarded to the source DeNB before the handover occurs. Suchradio resource information may include the MobilityControlInfo IE. Thesecurity configuration may be the SecurityConfigHO information element.

Once the source DeNB 1514 receives the measurement report from the RN,it sends out the handover command to the RN using the stored mobilitycontrol information while sending the handover request message to thetarget DeNB at the same time. This enables the RN to access the targetDeNB quickly without the source DeNB 1514 waiting for the handoverrequest acknowledgement message.

For relay architecture alternatives 2, 3 and 4, additionalfunctionalities such as the RN P-GW/S-GW, relay gateway, among othersmay need to be located at the target eNB 1516 to support the RN. Withthe existing handover procedures, source DeNB 1514 does not haveknowledge of the neighboring eNB's RN support capability. Even if thetarget eNB 1516 does not have the capability of supporting the RN, thesource DeNB will still request RN handover to that cell until therequest is rejected. However, this results in an undesired handoverdelay. To avoid such inappropriate handover requests, the eNBs may beinformed if the neighboring eNBs RN support capability. This may be doneby providing a relay support indicator through the X2 setup request andX2 setup response messages to convey the information, for example.

In a further alternative embodiment, in order to realize fast RNhandover, the RN may itself initiate the handover process by directlyaccessing the target DeNB after sending the measurement report. Toenable the RN to access the target DeNB, the source DeNB may sendconfiguration parameters such as mobility control information andsecurity configuration of the neighboring DeNBs to the RN before the RNaccesses the target DeNB.

One or multiple dedicated RACH preambles and C-RNTIs for the RN may bereserved at all eNBs that plans to serve the RN. To minimize the packetloss, the source DeNB starts to buffer packets after it receives themeasurement report from the RN.

Reference is now made to FIG. 16, in which the source DeNB sends thehandover request message to the target DeNB after receiving the RNmeasurement report. The target DeNB may receive the handover completemessage before receiving the handover request message with the RNinitiated handover approach. In this case, the target DeNB may hold thereceived handover complete message until the handover request messagearrives. To help the target DeNB to identify whether the received HORequest and handover complete messages are for the same RN, additionalinformation may be included in the handover request and handovercomplete messages such as the source DeNB cell ID and RNC-RNTI in thesource DeNB.

Thus, referring to FIG. 16, communication occurs between UE 1610, RN1612, source DeNB 1614, target DeNB 1616, MME 1618 and S-GW/P-GW 1620.

The RN receives configuration parameters from the source DeNB 1614, asshown by arrow 1628. The RN sends the measurement report, as shown byarrow 1630 and further sends an RRC connection reconfiguration completemessage directly to target DeNB 1616, as shown by arrow 1632.

As a result of receiving the measurement report at arrow 1630, sourceDeNB 1614 sends the handover request, shown by arrow 1634 to target DeNB1616 and target DeNB 1616 then sends a handover request acknowledgement,as shown by arrow 1636.

The RN path switch then occurs as shown by arrow 1640 and the remainingsteps as illustrated above with regard to the first step of the handoverare completed as described above. Namely, packet forwarding occurs, asshown at arrow 1650, the SN status transfer message is sent from sourceDeNB 1614 to target DeNB 1616, shown by arrow 1654, and the target DeNB1616 sends an RN context release message to source DeNB 1614, shown byarrow 1656

Unlike existing handover procedures, where the target eNB requests pathswitch after receiving the handover complete message from the UE, herethe target DeNB 1616 requests the RN path switch as shown by arrow 1640after receiving the handover request message from the source DeNB.

In a further alternative, when a mobile RN first connects with thesource DeNB, the source DeNB could indicate to the next potential targetDeNB through the X2 interface that a handover may soon occur. Thus,potential target DeNBs could prepare to receive RN initiated handoverssuch as the dedicated preambles and also prepare for the radio resource.

RN initiated handover reduces handover failure occurrence caused by fastdegrading received signal from the source DeNB in a high speed scenarioin some examples. In such a high speed scenario, handover failure isoften incurred by the RN experiencing radio link failures with theserving DeNB before the handover command is issued.

Group Mobility Procedure

In the second and fourth alternatives described above, for the UEs underthe RN, cell context information needs to be transferred from the sourceDeNB to the target DeNB. Additionally, the target DeNB may also need torequest a UE path switch to switch the UE downlink GTP tunnel towardsthe target DeNB. Sending multiple handover requests in the path switchfor each UE requires significant backhaul bandwidth. Instead ofperforming UE mobility procedures individually, in one embodiment the UEmobility may be handled as a group to avoid access handover signaling.Specifically, each handover has a handover overhead and thus groupingthe handovers for the UEs would save some of that overhead.

Reference is now made to FIG. 17, in which communications occur betweenvarious ones of UE 1710, RN 1712, source DeNB 1714, target DeNB 1716,MME 1718, and S-GW/P-GW 1720.

In the embodiment of FIG. 17, RN 1712 sends a measurement report, shownby arrow 1730 to source DeNB 1714.

Source DeNB then sends the group handover request for the RN and all theUEs under that RN to target DeNB 1716. Such a group handover request isshown by arrow 1732. Thus, the handover request for the RNs and UEs arecontained in one group handover request message. Correspondingly, thetarget DeNB then accepts or rejects on a per UE bearer in a grouphandover request acknowledgement message, shown by arrow 1734. Thesource DeNB 1714 could start forwarding UE packets afterwards.

Source DeNB 1714 then sends an RRC connection reconfiguration message toRN 1712, shown by arrow 1736, and starts the packet forwarding, shown byarrow 1738.

The source DeNB 1714 then sends a group SN status transfer for the RNsand the UEs to target DeNB 1716, shown by arrow 1740.

The RN 1712 can then send an RRC connection reconfiguration complete totarget DeNB 1716, as shown by arrow 1742, and the RN path switch canoccur subsequently between the target DeNB and the MME 1718, as shown byarrow 1744.

Target DeNB further sends an RN context release to source DeNB 1714, asshown by arrow 1746, and then a group path switch occurs between targetDeNB 1716 and the S-GW/P-GW 1720, as shown by arrow 1750.

The target DeNB then can send a group context release for the UEs, shownby arrow 1752, to source DeNB 1714.

The embodiment of FIG. 17 has the same second stage shown by box 1760 asdescribed above. Specifically, the S1 interface is setup, shown by arrow1762, and then the X2 interface is setup, shown by arrow 1764.Subsequently, target DeNB 1716 sends an eNB configuration update messageto source DeNB 1714, shown by arrow 1766. Source DeNB 1714 then sends aneNB configuration update acknowledgement, shown by arrow 1768.

Thus, in accordance with FIG. 17, after the RN is successfully attachedto the target DeNB as a UE, the target DeNB requests the RN path switchas well as UEs path switch. UEs belonging to the same MME can beincluded in one group path switch request message instead of requestingthe path switch for each UE individually. When the path switch requestacknowledgement for the RN and UEs is received at the target DeNB, thetarget DeNB notifies the source DeNB to release the RN context and UEcontext. The group path switch acknowledgement message and group contextrelease message can also be used to facilitate the UE group mobility.

After the RN establishes the S1/X2 interface with target DeNB, the RNhandover and group mobility procedure is further completed.

In one embodiment, the steps of box 1760 can be processed in parallelwith the RN/UE path switch in order to further reduce handover latency.

From FIG. 17, handover messages that may be enhanced to modify the groupmobility procedures are: the handover request message; handover requestacknowledgement message; SN status transfer message; path switch requestmessage; path switch request acknowledgement message; UE context releasemessage; handover complete message if handover complete message is usedto include UE contexts. These messages can be sent in the form of groupmessage which contains multiple UE information.

By encapsulating mobile UEs information in one group message, thehandover procedure is simplified and thereby the network nodes areoperated in an efficient manner. Network signaling overhead as well assignaling delay may be reduced as a result of the simplified procedure.

RN Group Mobility

Further, in some embodiments such as in a high speed train scenario,multiple RNs may be included within one train. For example, one relaymay serve one carriage in such a deployment scenario. It accordance withthe above deployment, the set of RNs move together. This characteristiccan be taken advantage of in a handover design as well. For example, thecontrol plane handover steps do not necessarily need to be repeated Ntimes, one for each RN. Rather, common steps may be performed by asingle lead relay node on behalf of the entire RN group.

The above may be done by assigning a group identifier to the RN group.Generally, a lead RN may be the first RN in the moving direction. Inorder to ensure robust connections during handover, a backup RN may beassigned to perform the handover procedure in case the lead RN fails. Inthe case that the mobile relays are deployed on high speed train, forexample, the RN group could be formed for the RNs that are located onadjacent carriages. Multiple RN groups may be formed for longer trainswith a number of carriages.

Alternatively, the DeNB may act as an anchor node for the RN grouphandover. One RN in the RN group may need to send measurement reports tothe DeNB. As the DeNB receives the measurement reports, it sends thegroup handover request message to the target DeNB, including the RNcontext for all RNs in the RN group.

Correspondingly, the target DeNB would include the handover command forall RNs in the RN group in the handover request acknowledgement message.

The handover command may be sent to the RN's using the group identifiersso that the RNs in the same group would receive the handover command atthe same time. Further, one dedicated random access preamble may beassigned to the RN group to be shared among the RNs. The RNs can use thesame dedicated random access preamble but perform random access channelcommunications at different timing offsets.

The above has the benefit of reducing over-the-air traffic andcontrol-plan signaling. The grouping of the RNs also saves resourcessuch as reserved dedicated random access preambles. In the user-plane,data forwarded for each individual RNs UE data would still be doneindividually.

The above may be implemented by any network element. A simplifiednetwork element is shown with regard to FIG. 18.

In FIG. 18, network element 1810 includes a processor 1820 and acommunications subsystem 1830, where the processor 1820 andcommunications subsystem 1830 cooperate to perform the methods describedabove.

Further, the above may be implemented by any UE. One exemplary device isdescribed below with regard to FIG. 19.

UE 1900 is typically a two-way wireless communication device havingvoice and data communication capabilities. UE 1900 generally has thecapability to communicate with other computer systems on the Internet.Depending on the exact functionality provided, the UE may be referred toas a data messaging device, a two-way pager, a wireless e-mail device, acellular telephone with data messaging capabilities, a wireless Internetappliance, a wireless device, a mobile device, or a data communicationdevice, as examples.

Where UE 1900 is enabled for two-way communication, it may incorporate acommunication subsystem 1911, including both a receiver 1912 and atransmitter 1914, as well as associated components such as one or moreantenna elements 1916 and 1918, local oscillators (LOs) 1913, and aprocessing module such as a digital signal processor (DSP) 1920. As willbe apparent to those skilled in the field of communications, theparticular design of the communication subsystem 1911 will be dependentupon the communication network in which the device is intended tooperate. The radio frequency front end of communication subsystem 1911can be any of the embodiments described above.

Network access requirements will also vary depending upon the type ofnetwork 1919. In some networks network access is associated with asubscriber or user of UE 1900. A UE may require a removable useridentity module (RUIM) or a subscriber identity module (SIM) card inorder to operate on a CDMA network. The SIM/RUIM interface 1944 isnormally similar to a card-slot into which a SIM/RUIM card can beinserted and ejected. The SIM/RUIM card can have memory and hold manykey configurations 1951, and other information 1953 such asidentification, and subscriber related information.

When required network registration or activation procedures have beencompleted, UE 1900 may send and receive communication signals over thenetwork 1919. As illustrated in FIG. 19, network 1919 can consist ofmultiple base stations communicating with the UE.

Signals received by antenna 1916 through communication network 1919 areinput to receiver 1912, which may perform such common receiver functionsas signal amplification, frequency down conversion, filtering, channelselection and the like. A/D conversion of a received signal allows morecomplex communication functions such as demodulation and decoding to beperformed in the DSP 1920. In a similar manner, signals to betransmitted are processed, including modulation and encoding forexample, by DSP 1920 and input to transmitter 1914 for digital to analogconversion, frequency up conversion, filtering, amplification andtransmission over the communication network 1919 via antenna 1918. DSP1920 not only processes communication signals, but also provides forreceiver and transmitter control. For example, the gains applied tocommunication signals in receiver 1912 and transmitter 1914 may beadaptively controlled through automatic gain control algorithmsimplemented in DSP 1920.

UE 1900 generally includes a processor 1938 which controls the overalloperation of the device. Communication functions, including data andvoice communications, are performed through communication subsystem1911. Processor 1938 also interacts with further device subsystems suchas the display 1922, flash memory 1924, random access memory (RAM) 1926,auxiliary input/output (I/O) subsystems 1928, serial port 1930, one ormore keyboards or keypads 1932, speaker 1934, microphone 1936, othercommunication subsystem 1940 such as a short-range communicationssubsystem and any other device subsystems generally designated as 1942.Serial port 1930 could include a USB port or other port known to thosein the art.

Some of the subsystems shown in FIG. 19 perform communication-relatedfunctions, whereas other subsystems may provide “resident” or on-devicefunctions. Notably, some subsystems, such as keyboard 1932 and display1922, for example, may be used for both communication-related functions,such as entering a text message for transmission over a communicationnetwork, and device-resident functions such as a calculator or tasklist.

Operating system software used by the processor 1938 may be stored in apersistent store such as flash memory 1924, which may instead be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile memory such as RAM 1926. Received communication signals mayalso be stored in RAM 1926.

As shown, flash memory 1924 can be segregated into different areas forboth computer programs 1958 and program data storage 1950, 1952, 1954and 1956. These different storage types indicate that each program canallocate a portion of flash memory 1924 for their own data storagerequirements. Processor 1938, in addition to its operating systemfunctions, may enable execution of software applications on the UE. Apredetermined set of applications that control basic operations,including at least data and voice communication applications forexample, will normally be installed on UE 1900 during manufacturing.Other applications could be installed subsequently or dynamically.

Applications and software may be stored on any computer readable storagemedium. The computer readable storage medium may be a tangible or intransitory/non-transitory medium such as optical (e.g., CD, DVD, etc.),magnetic (e.g., tape) or other memory known in the art.

One software application may be a personal information manager (PIM)application having the ability to organize and manage data itemsrelating to the user of the UE such as, but not limited to, e-mail,calendar events, voice mails, appointments, and task items. Naturally,one or more memory stores would be available on the UE to facilitatestorage of PIM data items. Such PIM application may have the ability tosend and receive data items, via the wireless network 1919. Furtherapplications may also be loaded onto the UE 1900 through the network1919, an auxiliary I/O subsystem 1928, serial port 1930, short-rangecommunications subsystem 1940 or any other suitable subsystem 1942, andinstalled by a user in the RAM 1926 or a non-volatile store (not shown)for execution by the processor 1938. Such flexibility in applicationinstallation increases the functionality of the device and may provideenhanced on-device functions, communication-related functions, or both.For example, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing the UE 1900.

In a data communication mode, a received signal such as a text messageor web page download will be processed by the communication subsystem1911 and input to the processor 1938, which may further process thereceived signal for output to the display 1922, or alternatively to anauxiliary I/O device 1928.

A user of UE 1900 may also compose data items such as email messages forexample, using the keyboard 1932, which may be a complete alphanumerickeyboard or telephone-type keypad, among others, in conjunction with thedisplay 1922 and possibly an auxiliary I/O device 1928. Such composeditems may then be transmitted over a communication network through thecommunication subsystem 1911.

For voice communications, overall operation of UE 1900 is similar,except that received signals would typically be output to a speaker 1934and signals for transmission would be generated by a microphone 1936.Alternative voice or audio I/O subsystems, such as a voice messagerecording subsystem, may also be implemented on UE 1900. Although voiceor audio signal output is generally accomplished primarily through thespeaker 1934, display 1922 may also be used to provide an indication ofthe identity of a calling party, the duration of a voice call, or othervoice call related information for example.

Serial port 1930 in FIG. 19 would normally be implemented in a personaldigital assistant (PDA)-type UE for which synchronization with a user'sdesktop computer (not shown) may be desirable, but is an optional devicecomponent. Such a port 1930 would enable a user to set preferencesthrough an external device or software application and would extend thecapabilities of UE 1900 by providing for information or softwaredownloads to UE 1900 other than through a wireless communicationnetwork. The alternate download path may for example be used to load anencryption key onto the device through a direct and thus reliable andtrusted connection to thereby enable secure device communication. Aswill be appreciated by those skilled in the art, serial port 1930 canfurther be used to connect the UE to a computer to act as a modem.

Other communications subsystems 1940, such as a short-rangecommunications subsystem, is a further optional component which mayprovide for communication between UE 1900 and different systems ordevices, which need not necessarily be similar devices. For example, thesubsystem 1940 may include an infrared device and associated circuitsand components or a Bluetooth™ communication module to provide forcommunication with similarly enabled systems and devices. Subsystem 1940may further include non-cellular communications such as WiFi or WiMAX.

The embodiments described herein are examples of structures, systems ormethods having elements corresponding to elements of the techniques ofthis application. This written description may enable those skilled inthe art to make and use embodiments having alternative elements thatlikewise correspond to the elements of the techniques of thisapplication. The intended scope of the techniques of this applicationthus includes other structures, systems or methods that do not differfrom the techniques of this application as described herein, and furtherincludes other structures, systems or methods with insubstantialdifferences from the techniques of this application as described herein.

The invention claimed is:
 1. A method for managing a relay node that ismoving relative to a source network node, the method comprising:receiving parameters of a target network node from a source network nodeat the relay node; sending a measurement report from the relay node tothe source network node; immediately after sending the measurementreport, initiating a direct attachment of the relay node to the targetnetwork node; and after initiating the direct attachment, detaching therelay node from the source network node.
 2. The method of claim 1,further comprising sending a measurement report to the source targetnetwork node before initiating the direct attachment.
 3. The method ofclaim 1 wherein the initiating the direct attachment includes accessingthe target network node with a dedicated RACH preamble.
 4. The method ofclaim 1 wherein the initiating the direct attachment includes accessingthe target network node with a predefined identifier for the relay node.5. The method of claim 1 wherein the parameters of the target networknode include mobility control information.
 6. The method of claim 1wherein the parameters of the target network node include securityconfiguration information.
 7. A relay node configured to move relativeto a source network node, the relay node comprising: a processor; and acommunications subsystem, wherein the processor and communicationssubsystem cooperate to: receive parameters of a target network node fromthe source network node at the relay node; send a measurement reportfrom the relay node to the source network node; immediately aftersending the measurement report, initiate a direct attachment of therelay node to the target network node; and after the direct attachmentis initiated, detach the relay node from the source network node.
 8. Therelay node of claim 7 wherein the initiating the direct attachmentincludes accessing the target network node with a dedicated RACHpreamble.
 9. The relay node of claim 7 wherein the initiating the directattachment includes accessing the target network node with a predefinedidentifier for the relay node.
 10. The relay node of claim 7 wherein theparameters of the target network node include mobility controlinformation.
 11. The relay node of claim 7 wherein the parameters of thetarget network node include security configuration information.